Chemical Nomenclature - Weebly · Chemical Nomenclature 396 Laying the Foundation in Chemistry 13...

Chemical Nomenclature

396 Laying the Foundation in Chemistry

13


Naming and Writing Chemical Formulas

Writing chemical formulas will open your eyes to the chemical world! Once you are able to write

correct chemical formulas, there are four naming systems you will need to master. The trick lies in

recognizing which naming system to use! Use the following guidelines when making your decision

about how to name compounds.

• If the compound starts with H, it is an acid. Use the Naming Acids rules.

• If the compound starts with C and contains quite a few H’s and perhaps some O, it is organic. Use

the Naming Organic Compound rules.

• If the compound starts with a metal it is most likely ionic. Use the Naming Binary Ionic Compounds

rules.

• If the compound starts with a nonmetal other than H or C, use the Naming Binary Molecular

Compounds rules.

It is essential that you memorize some common polyatomic ions. Polyatomic ions are groups of atoms

that behave as a unit and possess an overall charge. If more than one group is needed to balance a

formula, the group must be enclosed in parentheses before adding the subscripts. You need to know

their names, formulas and charges. If you learn the nine that follow, you can get many others from

applying two simple patterns! These nine are grouped by charge to make the memory work easier.

Name of Polyatomic Ion: Formula & Charge:

Ammonium ion NH4+

Acetate ion C2H3O2-

Cyanide ion CN-

Hydroxide ion OH-

Nitrate ion NO3-

Chlorate ion ClO3-

Sulfate ion SO42-

Carbonate ion CO32-

Phosphate ion PO43-

Pattern 1: The -ates “ate” one more oxygen than the –ites however, their charge doesn’t change as a

result. For instance, if you know nitrate is NO3-, then nitrite is NO2

-. If you know phosphate is PO4

3-,

then phosphite is PO33-

. You can also use the prefixes hypo- and per- with the chlorate series.

Perchlorate, ClO4-, was really “hyper and -ate yet another oxygen” when compared to chlorate, ClO3

-.

Hyopchlorite is a double whammy. It is –ite and therefore “ate” one less oxygen than chlorate and it is

hypo- which means “below” so it “ate” even one less oxygen than plain chlorite so its formula is ClO-.

You can substitute the other halogens for chlorine and make similar sets of this series.

13 Chemical Nomenclature

Laying the Foundation in Chemistry 397

Pattern 2: The -ates with charges less than negative one, meaning ions with charges of -2, -3, etc., can

have an H added to them to form new polyatomic ions. For each H added the charge is increased by a

+1. For instance, CO32-

can have an H added and become HCO3-. HCO3

- is called either the bicarbonate

ion or the hydrogen carbonate ion. Since phosphate is negative three, you can add one or two hydrogens

to make two new polyatomic ions, HPO42-

and H2PO4-. The names are hydrogen phosphate and

dihydrogen phosphate, respectively. If you continue adding hydrogen ions until you reach neutral,

you’ve made an acid! That means you need to see the Naming Acids rules.

Pattern 3: Use of the following periodic table will also come in handy. Notice the simple patterns for

determining the most common oxidation states of the elements based on their family’s position on the

periodic table. Notice the IA family is +1 while the IIA family is +2. Skip across to the IIIA family,

and notice that aluminum is +3. Working backwards from the halogens or VIIA family, they are most

commonly -1 while the VI A family is -2 and the VA family is -3. The IV A family is “wishy-washy”,

and can be several oxidation states, the most common being ± 4.

NAMING ACIDS

How do I know it’s an acid? The compound’s formula begins with a hydrogen, H, and water doesn’t

count. Naming acids is extremely easy, if you know your polyatomic ions. There are three rules to

follow:

• H + element: If the acid has only one element following the H, then use the prefix hydro- followed

by the element’s root name and an -ic ending. HCl is hydrochloric acid. H2S is hydrosulfuric acid.

When you see an acid name beginning with “hydro”, think “Caution, element approaching!” (HCN

is an exception since it is a polyatomic ion without oxygen, and it is named hydrocyanic acid.)

• H + -ate polyatomic ion: If the acid has an “-ate” polyatomic ion after the H, then it makes an “-ic”

acid. H2SO4 is sulfuric acid.

• H + -ite polyatomic ion: If the acid has an -“ite” polyatomic ion after the H, then it makes an “-ous”

acid. H2SO3 is sulfurous acid.



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When writing formulas for acids you must have enough H+ added to the anion to make the compound

neutral.

NAMING ORGANIC COMPOUNDS

How do I know it’s organic? The formula will start with a C followed by hydrogens and may even

contain some oxygen. Most of the organic carbons you will encounter will be either hydrocarbons or

alcohols. These are the simplest of all to name! Memorize the list of prefixes in Table B found in the

conclusion questions. The prefixes correspond to the number of carbons present in the compound and

will be the stem for each organic compound. Notice that the prefixes are standard geometric prefixes

once you pass the first four carbons. This silly statement will help you remember the order of the first

four prefixes since they are not ones you are familiar with: “Me Eat Peanut Butter.” This corresponds

to meth-, eth-, prop-, and but- which correspond to 1, 2, 3, and 4 carbons, respectively. Now that we

have a stem, we need an ending. There are four common hydrocarbon endings that you will need to

know. The ending changes depending on the structure of the molecule.

• -ane - alkane (all single bonds & saturated) CnH2n+2; The term saturated means that the compound

contains the maximum number of hydrogen atoms.

• -ene = alkene (contains one double bond & unsaturated) CnH2n; The term unsaturated means that in

the compound hydrogens have been removed in order to create a multiple bond.

• -yne ≡ alkyne (contains one triple bond & unsaturated) CnH2n-2; The term polyunsaturated means

that the compound contains more than one double or triple bond.

• -ol – alcohol (one H is replaced with a hydroxyl group, -OH group, to form an alcohol) CnH2n+1; Do

not be fooled—this looks like a hydroxide group, but is not! It does not make this hydrocarbon an

alkaline or basic compound. Do not name these as a hydroxide! C2H6 is ethane while C2H5OH is

ethanol.

NAMING BINARY IONIC COMPOUNDS

How do I know it is ionic? The formula will begin with a metal cation or the ammonium cation. The

ending is often a polyatomic anion. If only two elements are present, they are usually from opposite

sides of the periodic table, like KCl. If the metal is a transition metal, be prepared to use a Roman

numeral indicating which oxidation state the metal is exhibiting. Silver (Ag), cadmium (Cd) and zinc

(Zn) are exceptions to the Roman numeral rule because their charges are constant. In order to remember

their charges, place their symbols in alphabetical order and then they are in order; +1, +2, +2.

In order to name these compounds, first let’s name the ions.



Naming positive ions: Metals commonly form cations.

• Monatomic positive ions in Group A are named by simply writing the name of the metal from which

it is derived. Al3+

is the aluminum ion.

• Transition metals often form more than one positive ion so Roman numerals (in parentheses) follow

the ion=s name. Cu2+

is copper (II) ion. Remember the exceptions listed above.

• NH4+

is the ammonium ion. It is the only positive polyatomic ion that you will encounter.

Naming negative ions: Nonmetals commonly form anions. Most of the polyatomic ions are also

negatively-charged.

• Monatomic negative ions are named by adding the suffix -ide to the stem of

the nonmetal’s name. Halogens are called the halides. Cl- is the chloride ion.

• Polyatomic anions are given the names of the polyatomic ion. You must memorize these. NO2- is

the nitrite ion.

Naming the Compound: The + ion (cation) name is given first remembering that transition metals will

contain the Roman numeral indicating its charge followed by the name of the negative ion (anion). No

prefixes are used.

NAMING BINARY MOLECULAR COMPOUNDS

How will I know it is a molecular compound? It will be a combination of nonmetals, both lying near

each other on the periodic table. No polyatomic ions will be present! Use the following set of prefixes

when naming molecular compounds.

Subscript Prefix

1 Mono-

[usually used only on the second element; such as

carbon monoxide or nitrogen monoxide]

2 di-

3 tri-

4 tetra-

5 penta-

6 hexa-

7 hepta-

8 octa-

9 nona-

10 deca-

Naming the Compound: The + ion name is given first followed by the name of the negative ion. Use

prefixes to indicate the number of atoms of each element. Don’t forget the –ide ending! If the second

element’s name begins with a vowel, then the “a” at the end of the prefix is usually dropped. N2O5 is

dinitrogen pentoxide not dinitrogen pentaoxide. PCl5 is phosphorous pentachloride not phosphorous

pentchloride.



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FORMULA WRITING

Naming is the trickiest part! Once you’ve been given the name, the formula writing is easy as long as

you have memorized the formulas and charges of the polyatomic ions. The prefixes of a molecular

compound make it really easy to write the formula since the prefix tells you how many atoms are present

for each element. Roman numerals are your friend; they tell you the charge on the transition metal.

Remember that Ag, Cd, & Zn are usually not written with a Roman numeral; you must know their

charges. The most important thing to remember is that, the sum of the charges must add up to zero in

order to form a neutral compound. The crisscross method is very useful—the charge on one ion

becomes the subscript on the other. If you use this method, you must always check to see that the

subscripts are in their lowest ratio! Here are some examples:

potassium oxide � K1+

O2-

� K1 O

2 � K2O

iron (III) chlorate � Fe3+

ClO31- � Fe

3 ClO3

1� Fe(ClO3)3

tin (IV) sulfite � Sn4+

SO32-

� Sn4 SO3

2 � Sn2(SO3)4 � Sn(SO3)2

zinc acetate � Zn2+

C2H3O21-

� Zn 2

C2H3O21 � Zn(C2H3O2)2

COORDINATION CHEMISTRY NOMENCLATURE

These are actually quite fun! The rules are simple and you will really feel like you are speaking

chemistry. Square brackets are used to enclose a complex ion or neutral coordination species. A

complex ion is composed of a single central atom or ion with other atoms or molecules attached. The

atoms or molecules attached are known as ligands. The number of ligands attached is called the

coordination number of the complex ion. The naming of complex cations and complex anions is similar,

except that anions are always made to end in -ate. Coordination compounds, like other ionic

compounds, are named with the cation preceding the anion regardless of which (if either) one of them is

a complex ion.

The rules for naming complex ions or compounds are as follows:

• As with any ionic compound, the cation is named before the anion.

• In naming a complex ion, the ligands are named before the central metal ion.

• In naming ligands, an “-o” is added to the root name of any anion. For example, the halides as

ligands are called fluoro, chloro, bromo, and iodo; hydroxide is hydroxo; cyanide is cyano; nitrite is

nitrito, etc. If the ligands are neutral, omit the “-o” ending. Neutral ligands take the name they

normally use as neutral molecules. There are four exceptions which must be memorized: H2O as a ligand is known as aqua, NH3 is named ammine [note the “mm” in the spelling so it is not confused

with the functional group –NH2, an amine group], CO is named carbonyl, and NO is nitrosyl.

• The number of each kind of ligand is specified by the usual Greek prefix: mono-, di-, tri-,

tetra-, penta-, and hexa-.

• The oxidation state of the central metal atom is designated by a Roman numeral in parentheses.



• When more than one type of ligand is present, they are named in alphabetic order with no regard for

the Greek (numerical) prefix.

• If the complex has a negative charge, the suffix -ate is added to the name of the metal. When a

Latin symbol is used for the element, the element takes the Latin name in complex anions but not in

complex cations. For example, [Cu(NH3)4]2+

is called the tetraamminecopper(II)

ion but [Cu(CN)6]4-

is called the hexacyanocuprate(II) ion. Likewise [Al(NH3)6]3+

is called

the hexaamminealuminum(III) ion but [Al(OH)4]- is called the tetrahydroxoaluminate(III) ion.

Common Neutral Ligands

Formula Name

H2O aqua

NH3 ammine

CO carbonyl

NO nitrosyl

Common Anion Ligands

Formula Name

F- fluoro

Cl-

chloro

Br- bromo

I-

iodo

OH-

hydroxo

CN-

cyano

SCN- thiocyano

S2O32-

thiosulfate

C2O42-

oxalato

Latin Names Used for Some Metal Ions in Anionic Complex Ions

Iron ferrate

Copper cuprate

Lead plumbate

Silver argentate

Gold aurate

Tin stannate



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PURPOSE To master the skill of writing and naming chemical formulas.

MATERIALS scissors

colored markers: blue, red, yellow, green, purple, pink

PROCEDURE 1. Carefully cut out the shapes on Template 1. Group them by similar charge or oxidation state.

2. Trace over the symbol and oxidation state of each element using colored markers and apply the color

scheme below:

Color Oxidation State

Blue +1

Red -1

Yellow +2

Green -2

Purple +3

Pink -3

3. Notice how the models fit together. If an element has a 3+ oxidation state, it requires three elements

with a 1- oxidation state to create a complete compound.

4. Carefully cut out the shapes on Template 2. Each carbon model has 4 inward notches. The model

“bonds” found on Template 2 are for connecting the carbons. These shapes will be used to help you

with organic compounds. There is no need to color them.

5. Review the rules for naming acids and complete Table A on your student answer sheet. Use the

models you created from Template 1 as needed. Supply either the acid’s name or its formula to

complete Table A.

6. Review the rules for naming organic hydrocarbons and alcohols. Use your models from Template 2

as needed. Fill in the missing formulas and names for each compound in Table B.

7. Review the rules for naming binary ionic and molecular compounds and complete the table below.

Use the models you created from the template as needed. Supply the compound’s formula and

name to complete Table C. If the charge or oxidation state is missing from the table, it is because

you should already know them or be able to determine them due to their position in the periodic

table.

Safety Alert 1. Use care when handling scissors.


Name _____________________________________

Period ____________________________________


Chemical Nomenclature Naming and Writing Chemical Formulas

All You Really Need to Know About Chemical Names and Formulas SUMMARIZED In this flowchart, D and J in the general formula DxJy can represent atoms, monatomic ions, or

polyatomic ions.



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CONCLUSION QUESTIONS

Table A

Acid Formula Acid Name:

HCl

hypochlorous acid

chlorous acid

chloric acid

perchloric acid (‘hyperchloric acid)

HNO3

hydrobromic acid

H3PO4

H3PO3

hydrocyanic acid

HC2H3O2

carbonic acid

hydroiodic acid

HF

Table B

# of carbon atoms = n prefix or stem -ane

CnH2n+2

-ene

CnH2n

-yne

CnH2n-2

-anol

CnH2n+1OH

1 meth-

None here because you

must have at least 2

carbons !

CH3OH

2 eth-

3 prop- C3H6

4 but-

5 pent- C5H12

6 hex-

7 hept- C7H15OH

8 oct- C8H14

9 non-

10 dec-



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Table D

Formula Name

tetrahydroxoaluminate (III) ion

[Ag(NH3)2]+

tetrahydroxozincate (II) ion

[Zn(NH3)4]2+

tetramminecopper(II) ion

[FeSCN]2+

[FeSCN]Cl2

tetramminecadmium(II) ion

[Ag(CN)2]-

Mg [Ag(CN)2]-2

dibromodichlorodiiodocuprate(II) ion

[Co(NH3)5Cl]Cl2

potassium hexacyanoferrate(III)

triamminebromoplatinum(II) chloride

[Cu(Cl2Br2INH3)]4-

K3[Co(F)6]

[Co(NH3)6]Cl2

hexacyanoferrate(II)



Al3+

NH4+

Mn2+

H+

H+

H+

H+

H+

H+

Ag+

Cl-

NO3-

Br-

Pb2+

Cu+

Ba2+

N3-

O2-

S2-

SO42-

H+

H+

H+

H+

H+



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ClO-

C2H3O2-

PO33-

S2-

CO32-

ClO2-

ClO3-

ClO4-

F-

I-

CN-

PO43-



CCC C

C

C

C

C

C

C

CCH

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

OH

OH

OH

Use the models

below as single,

double and triple

bonds for connecting

carbons.

Chemical Nomenclature - Weebly · Chemical Nomenclature 396 Laying the Foundation in Chemistry 13...

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